This invention relates generally to a cutting tool and more particularly to a ball nose end mill, and an arrangement for retaining a replaceable cutting insert therein, especially an indexable cutting insert.
In conventional ball nose end mills cutting inserts are clamped in position by a retaining screw. A problem with this arrangement is that the accuracy of the initial location of the cutting edge of a cutting insert retained in the end mill is dependent on the accuracy with which the retaining screw is located in the end mill. Any play or clearance between the screw and the cutting insert results in a corresponding inaccuracy in the location of the cutting edge of the cutting insert.
A solution to this problem is proposed in U.S. Pat. No. 4,883,391, in accordance with which a clamping screw is provided with a cylindrical portion which is held in engagement with a cylindrical bore portion in the end mill. However, this solution calls for both a very accurately manufactured cylindrical portion on the screw and a correspondingly very accurately manufactured cylindrical bore portion in the end mill. Both of these requirements increase the cost of manufacture of the end mill as a whole. Furthermore, any inaccuracies introduced into these two cylindrical elements during use of the end mill, will introduce a corresponding inaccuracy in the location of the cutting edge of the cutting insert.
In accordance with the present invention there is provided a cutting tool assembly comprising a cutting insert holder and a cutting insert, the cutting insert holder comprising a clamping portion, at a front portion thereof, connected to a body portion;
the clamping portion comprising:
a lower clamping jaw having a lower peripheral surface and an upper surface;
an upper clamping jaw resiliently connected to the lower clamping jaw, the upper clamping jaw having a lower surface and an upper peripheral surface, the lower surface being provided with two elongated spaced apart substantially parallel grooves;
a through bore passing through the upper and lower clamping jaws, the through bore being internally threaded in one of the upper or lower clamping jaws; and
an insert receiving slot defined between the upper and lower clamping jaws; the cutting insert comprising:
an upper surface provided with two elongated spaced apart substantially parallel ridges;
a lower surface;
a peripheral side surface between the upper surface and the lower surface, the peripheral side surface being provided with at least one cutting edge;
a rake surface associated with the at least one cutting edge; and
a through bore passing through the cutting insert, from the upper surface to the lower surface;
wherein the cutting insert is retained in the insert receiving slot in a retained position by means of a screw which passes through the through bore in the upper and lower jaws of the insert holder and through the through bore in the cutting insert, and wherein in the retained position at least a portion of the lower surface of the cutting insert abuts at least a portion of the upper surface of the lower clamping jaw and the two elongated ridges in the upper surface of the cutting insert cooperate with the two elongated parallel grooves in the lower surface of the upper clamping jaw.
In accordance with a preferred embodiment of the present invention, the cutting insert is provided with at least one elongated recess in the peripheral side surface of the cutting insert adjacent a portion of the lower surface, and the upper surface of the lower clamping jaw is provided with an insert location surface and at least a portion of a substantially upright surface of the at least one elongated recess in the peripheral side surface of the cutting insert abuts the insert location surface in the upper surface of the lower clamping jaw.
Also in accordance with the present invention there is provided a cutting insert comprising:
an upper surface provided with two elongated spaced apart substantially parallel ridges;
a lower surface;
a peripheral side surface between the upper surface and the lower surface, the peripheral side surface being provided with at least one cutting edge;
a rake surface associated with the at least one cutting edge; and
a through bore passing through the cutting insert, from the upper surface to the lower surface.
Also in accordance with a preferred embodiment, the peripheral side surface of the cutting insert is provided with at least one elongated recess adjacent a portion of the lower surface.
In accordance with a preferred embodiment of the present invention, the two elongated grooves in the lower surface of the upper clamping jaw are located adjacent to and on either side of the through bore in the upper clamping jaw.
Further in accordance with a preferred embodiment of the present invention, the two elongated ridges in the upper surface of the cutting insert are located adjacent to and on either side of the through bore in the cutting insert
Still further in accordance with a preferred embodiment of the present invention, each of the two elongated ridges in the upper surface of the cutting insert have an indentation in a portion thereof.
Yet still further in accordance with a preferred embodiment of the present invention, the indentation is in a region adjacent the through bore in the cutting insert.
In accordance with one specific application, the cutting insert is generally oval in shape in a top view and is provided with two diametrically opposite sets of cutting edges.